In general, the engines used for vehicles or construction equipment include a cylinder and a piston that reciprocates inside the cylinder. The piston, a part for transmitting explosive pressure inside the cylinder to a crankshaft through a connecting rod, is exposed to high-temperature combustion gas as well as high combustion pressure, such that it may be easily damaged, such as fatigue failure or frictional wear due to thermal deformation, and fusion. For this reason, the piston has a specific cooling structure and an example of the structure is shown in FIG. 1.
Referring to FIG. 1, an oil gallery 2 is formed in a ring shape in a piston 1. Further, an oil intake port 3 is formed at a side of oil gallery 2, an oil exhaust port 4 is formed at the other side of oil gallery 2, and an oil jet 5 is disposed adjacent to oil intake port 3.
Cooling oil injected by the oil jet 5 flows into the oil gallery 2 through the oil intake port 3, circulates through the oil gallery 2, and is then discharged through the oil exhaust port 4. The cooling oil that flows as described above cools piston 1 by taking heat from the piston 1.
However, as shown in FIGS. 2 and 3, most of the oil injected from the oil jet 5 fails to flow into the oil gallery 2 through the oil intake port 3 and is discharged to the oil intake port 3 while hitting against the upper inner side of the oil gallery 2. Accordingly, only a small amount of the oil injected from the oil jet 5 flows into the oil gallery 2.
As described above, since the amount of the oil flowing into the oil gallery 2 is small, the amount of the oil circulating in oil gallery 2 decreases, such that the cooling efficiency of the piston 1 decreases. Further, the small amount of the oil flowing in the oil gallery 2 remains in the oil gallery 2 for a long time because it is difficult to move to the oil exhaust port 4, and the temperature of the oil in the oil gallery 2 correspondingly increases, such that the cooling efficiency of the piston 1 further decreases.
Meanwhile, the portion connected with the oil intake port 3 of oil gallery 2 is in contact with the low-temperature oil injected by the oil jet 5, such that the portion is more cooled than the other portions. For this reason, a temperature difference occurs in the piston 1 and thermal stress is exerted in the piston 1 due to the temperature difference, such that the durability decreases.
As described above, since not only the cooling efficiency of the piston with the oil gallery of the related art is low, but the thermal stress due to a temperature difference is exerted, resulting in the piston and other parts around the piston to be easily damaged.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.